[PATCH v3 1/8] lib/glob: normalize inverted character class ranges

[Josh Law]

When a character class range has its endpoints reversed (e.g., [z-a]),
the comparison a <= c && c <= b can never be true, so the range
silently matches nothing.  A pattern like "file[9-0]" intended to
match any digit would fail to match anything, with no indication
that the range is backwards.

Swap the endpoints when a > b so that inverted ranges behave the
same as their forward equivalents: [z-a] matches the same characters
as [a-z], and [9-0] matches the same as [0-9].  This is consistent
with how GNU fnmatch and other glob implementations handle reversed
ranges.

Signed-off-by: Josh Law <objecting@xxxxxxxxxxxxx>
---
 lib/glob.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/glob.c b/lib/glob.c
index 7aca76c25bcb..cb45a9a47f28 100644
--- a/lib/glob.c
+++ b/lib/glob.c
@@ -94,7 +94,13 @@ bool __pure glob_match(char const *pat, char const *str)
 						goto literal;
 
 					class += 2;
-					/* Any special action if a > b? */
+					/* Normalize inverted ranges like [z-a] */
+					if (a > b) {
+						unsigned char tmp = a;
+
+						a = b;
+						b = tmp;
+					}
 				}
 				if (a <= c && c <= b)
 					match = true;
-- 
2.34.1